Eerroresonant flip-flops



May 31, 1955 w. E. TRIEST FERRORESONANT FLIP-FLOPS 2 Sheets-Sheet 1Filed Aug. 25, 1953 FIG! CURRENT -L|NEAR EMPEDANCE TRIGGER FIG. 3

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-/-v5/vr0, By WILLIAM E. TR/EST JOHN ALDEN HALL A TTO/QNEV y 31, 1955 w.E. TRIEST 2,709,757

FERRORESONANT FLIP-FLOPS Filed Aug. 25, 1953 2 Sheets-Sheet 2 1 M i l hF/G,4 EB n fl A A A A A A A 3 70m 50 KC.

SOURCE OF TRIGGER PU LSES INVENTOR By WILL MM 5 TR/ES T J'OHN ALDEN HALLATTOENE 3 United States Patent O FERRORESONANT FLIP-.FLOPS Wiliiam E.Triest, Hyde Park, N. Y., assignor to International B s e achi esorporat on, New k, N. Y., a corporation of New York Application August25, 1953, Serial No. 376,490

7 m (CL 0 -8 This invention relates to electronic switching means andparticularly to means for selecting and enabling paths for thetransmission of electrical pulses.

In the art of electronic control where exceptionally high speedoperations are essential, information is transmitted by pulses and wheredifferent steady state current conditions are to be established this isaccomplished by triggering electronic tubes into operation. Staticdevices are employed since any mechanical movements as the operation ofswitches, manual or power driven or the operation of relays are notwithin the speed requirements for such electronic switching.

The object of the present invention is the provision of a flip-flopdevice having a sufiicient speed of operation for use in an electronicswitching system. The term flip-flop is commonly used in the electronicart to desigs nate a device which on alternate operations willsuccessively condition or enable two outgoing paths. For prior artdescriptions of such devices reference is made to Electronics, April1952, page 121, and, in the computer art to the Williams Patent2,502,360, column 6, lines 50 et seq.

In accordance with the present invention a peculiar phenomenon observedin electrical circuits carrying alternating current and includingtherein iron core coils is employed. This is spoken of as the jumpingphenomena in ferroresonance, for an application of which, reference ismade to the prior art disclosures in the Stacy and Krom Patent1,725,022, August 20, 1929. In the observation of these circuits it hasbeen noted that as the voltage applied to the circuit is steadilyincreased so does the current steadily increase until a point is reachedwhere the current suddenly leaves its steady advance and jumps to a muchgreater value. Also, when from this greater value the voltage is thensteadily decreased so does the current steadily decrease until a pointis reached where F the current suddenly jumps to a much lower value.

The object of the present invention is to improve the operation ofdevices depending on the principle of this phenomenon by providingcircuit means to exaggerate the effect so as to provide a great marginin the commer-. cial tolerances of the electrical components going intothe construction of such devices.

A feature of the invention is the use of a circuit having a pair ofparallel circuits each including a ferroresonant element, constructedand arranged to be mutually controlling whereby a circuit disturbancewill cause the current flow in both of said parallel circuits to jump,one in one direction and one in the other, and whereby the change incurrent value in each of said circuits will fortify the change in theother.

The extent to which the current change in one circuit fortifies thechange in the other is a measure of the speed of operation of thecircuit. Where a plurality of these flip-flops are interconnected toprovide a frequency divider, the speed of operation of each is acont-rolling factor in the limits of frequency values that may beapplied. Operations within kilocycle ranges are possible offerroresonance.

2,709,757 Patented May 31, 1955 with prior art devices and it would beuseful if the same operations could be extended into the megacycleranges but this requires smaller and smaller impedance values in thecircuit components so that regenerative or fortifying means have to beemployed.

A feature of the invention is the use of selected magnetic material inthe ferroresonant components of the circuits which have certain magneticcharacteristics tending to increase the rapidity of magnetic changes.Certain magnetic materials are known which have what may be describedgraphically as a substantially square hysteresis loop or one in whichthe change from magnetic energigation in one direction to correspondingenergization in the other is practically instantaneous. The rapidity ofthis change is a factor in the value of the potential induced in a coilwound about such magnetic material and therefore is a controlling factorin the tolerances that may be allowed in the practical construction ofthe device.

Another feature of the invention is the use of cross coupling means inthe said two parallel ferroresonant circuits. Thus when a circuitdisturbance is effected as by a triggering pulse in an associatedmagnetic element coil, the current in one branch will increase and thecurrent in the other branch will decrease. If the coils carrying thesebranch currents are cross coupled, then the total current or totalmagnetomotive force generated in one magnetic element will be increasedby the natural increase in cur rent in its principal winding and alsoincreased by the natural decrease in current in the other circuit by across coupling coil on the said magnetic element. By the same token themagnetomotive force generated in the other magnetic element will bedecreased by the natural decrease in current in its principal windingand also decreased by the natural inrease in current in the othercircuit by a cross coupling coil on the said magnetic element. This isanalogous to a regenerative effect since the efiect operates to fortifyitself whereby the speed of operation is greatly increased.

Other features will appear hereinafter.

The drawings consist of two sheets having six figures, as follows:

Fig. 1 is a graph showing the relation between voltage and current in analternating current ferroresonant circuit;

Fig. 2 is a schematic circuit diagram of a conventional ferroresonantflip-flop device used for purposes of explanation;

Fig. 3 is an idealized graph used in the description of the circuit ofFig. 2;

Fig. 4 is a representation of wave forms in different branches of thecircuit of Fig. 2;

Fig. 5 is a schematic circuit diagram of the arrangement of the elementsof the present invention, showing particularly the cross coupling coilsemployed in the manner about to be explained; and

Fig. 6 is a schematic circuit diagram showing how several ferroresonantflip-flop circuits may be connected in cascade as in a frequencydivider.

Ferroresonance is a phenomenon which has been observed in alternatingcurrent circuits having resistance, capacity and inductancecharacterized by non-linearity of inductance values generally producedby a coil inter-. linked with a magnetic circuit. Fig. 1 shows therelation between voltage and current in such a circuit and indicateswhat has been termed the jumping phenomenon This figure indicates thatas the voltage increases, the current likewise increases to a point awhere the current suddenly increases to the value at point I).Thereafter the current increases as the voltage increases toward thedirection of point e. If, while the circuit is in the stable conditionindicated by the curve from the point a through b toward 0, the voltage,or the current is decreased the point (I will be reached Where suddenlythe current value will be reduced to the value at e. Such a circuittherefore shows a rising value e a b c and a falling value c b d e 0 andhas two stable states 0 e and b c under any and all conditions, andstable states 0 e a and b c under rising values and c b d and e 0 underdiminishing values.

The jumping phenomenon of ferroresonance has been employed in circuitoperators known as ferroresonant flip-flops.

A flip-flop is a bistable circuit device which may be employed as ascale of two means, that is by a first pulse it may be driven from onestable state to another and by a succeeding pulse it may be driven backto the first stable state. It is a device finding use, by way ofexample, in the circuitry of chain and ring counters and in frequencydividers. Very high speed flip-flops are essential in the circuitry ofelectronic computers.

Fig. 2 illustrates the principle of operation of a ferroresonantflip-flop. The voltage E is any alternating current source including ahigh frequency source such as one generating radio frequency power. Theload consists of a common impedance 1 connected in series with twocircuits 2 and 3 connected in parallel relation with each other and eachcontaining a saturable core inductor, 4 and 5 respectively, and acapacity element, 6 and 7 respectively. Each saturable core inductor isprovided with an additional coil, 8 and 9 respectively, by means ofwhich the circuits may be triggered. Each of these two branch circuitsis capable of exhibiting ferroresonance as shown in Fig. 3. If voltage Eand common impedance 1 are properly chosen, E1 will be at a value Ex andone of the LC branches will be at state (2) with high current andconsequent high capacitor voltage, While the other branch will be instate (1) with low current and low capacitor voltage. The high currentin one resonant branch causes a voltage drop across the Z impedance 1which reduces the voltage across the L-C branches to Ex- Only one branchcan be in ferroresonance, since ferroresonance in both would produce anexcessive drop in Z1 and the voltage across L-C would be below thecritical voltage E01.

Assume initially that branch 2 is in state (1) and branch 3 is in state(2). Next assume a pulse signal to be transmitted over trigger A throughcoil 8. The inductance LA of coil 4 will decrease, and this branch willtend toward the ferroresonant condition. The increased voltage dropcross the Z impedance 1, due to higher current in branch 2, will reduceE1 below E01 and branch 3 will drop from state (2) to state (1).Simultaneously, branch 2 will be driven further into ferroresonance andwill go to state (2). Branch 2 will then remain in state (2) and branch3 will remain in state (1) until a signal appears at the trigger Bterminal.

Any conventional means, such as a crystal diode and a simple filtercircuit, may be used to obtain direct current levels from the EA tap 10and the EB tap 11.

By way of example, a circuit in the form of Fig. 3 might have Z in theform of a resistor of 100 ohms, CAXCB each of .005 mfd. and coils 4 and5 each 180 turns of wire on a core 1D constructed of 5 convolutions of.0007 inch tape wide of a magnetic material of high retentivity anddisplaying a particularly square hysteresis loop. The power source E maybe 100 kc. If the power source is applied, starting at E=0, it may beincreased until one of the branches becomes ferroresonant and thenadvanced just beyond this voltage when the circuit becomes stable.Trigger pulses of about 7 microseconds will flip the state of thecircuit and if the two coils 8 and 9 are connected to a single triggerconductor successive trigger pulses applied thereto would successivelychange the state of the two coils in the fashion of a scale of twodevice.

' Fig. 4 is a representation of the voltage EA and EB wave forms as thecircuit is triggered as indicated by the succession of trigger pulses.These pulses have been shown partly as following one another withregularity and partly in an irregular manner. In some circuits such as afrequency divider, the trigger pulses would follow one another with thegreatest regularity, whereas in other circuits, as in a computer, theymight be irregularly spaced.

Applicant has found that greatly improved operation may be achieved bymaking the ratio of EH1 to ELo as great as possible and he has achievedthis desirable goal by adding another coil to each saturable core andconnecting it to the other circuit as shown in Fig. 5 to provide adegree of cross coupling. By making the coils 12 and 13 of 75 turns eachand using in the circuit described the ratio Ear/Era is multiplied bythree. In addition, the series R3 resistor may be increased.

It has been determined that the current in the branch in state (1) is alagging current, characteristic of an inductive load, whereas thecurrent in the branch in state (2) is a leading current characteristicof a capacitive load.

The cross-coupling arrangement of the present device shown in Fig. 5makes use of the fact that the currents in branches 2 and 3 are ofopposite phase. A leading current flows in the ferroresonant branchwhile a lagging current flows in the other branch as above explained. ByWay of example, if branch 2 is ferroresonant, then the high leadingcurrent in the L E coil 13 will produce flux in core 15 to induce avoltage in the LB coil 16 that will oppose the lagging current therein.This results in a decrease in the current in branch 3 and an increase incurrent in branch 2, thus emphasizing the tendencies of the two circuitsand widening the gap between the values of the voltage drop across thecondensers CA and CB.

Thus conventional ferroresonant flip-flop circuits may be improved intheir operation by employing cross coupled coils on the saturable cores.

Fig. 6 is a schematic circuit diagram showing how two circuits of thetype of Fig. 5 may be connected in cascade to form a frequency divider.The source of alternating current 17 is shown, merely by way of example,as one having a frequency of 700 kc., while the source of triggeringpulses 18 is shown also, merely by way of example. as one having aperiodicity of 50 kc. One output lead 19, leads to a second circuit. Theperiodicity of the output would be one half the input, or 25 kc. Anartificial line or balancing network will be connected to the otheroutput 20 and this too would show an output of kc.

The output 21 of the second circuit is indicated as leading to a thirdcircuit where it may be used for further dividing the frequency or forany other purpose.

What is claimed is:

1. An alternating current circuit element having a linear impedance inseries with a circuit network comprising two like parallel branches,each said branch including a non-linear impedance element and each saidbranch having means to control the said non-linear impedance element ofthe other said branch.

2. An alternating current circuit element having a linear impedance inseries with a circuit network com prising two'like parallel branches,each said branch including linear and a non-linear impedance elementsand each said branch having means to control the said nonlinearimpedance element of the other said branch.

3. An alternating current circuit element having a resistance element inseries with a circuit network comprising two like parallel branches,each said branch including a capacitive element in series with an ironcored coil and each said branch also having in series a coil coupledwith said iron cored coil of said other branch.

4. An alternating current circuit element having a resistance element inseries with a circuit network comprising two like parallel branches,each said branch including a capacitive element in series with a coilmagnetically interlinked with an element having magnetic propertiescharacterized by a substantially rectangular hysteresis curve and eachsaid branch having in series another coil magnetically interlinked withthe said first coil of said other branch.

5. An alternating current circuit element having a linear impedance inseries with a circuit network comprising two like parallel branches eachincluding a linear and a non-linear impedance element and each saidbranch having means to control said non-linear impedance element of saidother branch, and a separate circuit for controlling said non-linearelements concurrently.

6. An alternating current circuit element having a linear impedanceelement in series with a circuit network comprising two like parallelbranches each including a linear and a non-linear impedance element andeach said branch having means to control the said non-linear impedanceelement of the other said branches, said elements being so proportionedthat a leading alternating current will flow in one of said branches anda lagging alternating current will flow in the other of said branches,and means for disturbing the said current flow conditions in said twobranches whereby the said conditions will become reversed.

7. An alternating current circuit element having a linear impedanceelement in series with a circuit network comprising two like parallelferroresonant circuits, whereby unlike currents will flow through saidcircuits, each having means for controlling the other and means fortransmitting pulses simultaneously into each said ferroresonant circuitswhereby said unlike current conditions become interchanged responsive toeach said pulse.

References Cited in the file of this patent UNITED STATES PATENTS2,653,254 Spitzer et al Sept. 22, 1953

